Is money earned from mediating car insurance for one's brother halal?

Commercial insurance is prohibited. However, if a person is forced into it, it is permissible for him to participate, and the sin falls upon the one who coerced him. If your brother's participation in the same company entails giving you a portion of the money, there is no objection to that, provided the company will give you this money from its profit and not add it to the subscriber you introduced to it. This is permissible because you guided someone to an act they were forced into. However, guiding a person who has a choice is not permissible because it is guiding to disobedience.